1. Field of Invention
The present invention generally relates to precooking shrimp for more effective machine peeling of various species of shrimp. More specifically, the invention relates to an apparatus for more effectively controlling the precooking operation by separating the precooking procedure into multiple distinct zones and controlling the temperature in each cooking zone. A porous conveyor belt conveys shrimp from a feeder tank at a temperature of approximately 40.degree. F. into zone 1 maintained at a temperature of 212.degree. F. and subsequently into zone 2 in which the temperature is maintained at 212.degree. F. and finally into zone 3 and optionally into zone 4 maintained at a temperature less than 212.degree. F. In zone 1 the mixture of air and steam from both above and below the shrimp will condense on the surface of the shrimp for control cooking in zone 1 in which the shrimp is heated to approximately 116.degree. F. In zone 2, the same cooking procedure raises the cooking temperature of the shrimp to approximately 173.degree. F. In zone 3, and optionally in zone 4, a controlled cooking atmosphere is maintained at 180.degree. F. to 212.degree. F. to permit equilibration of temperature of approximately 160.degree. F. in the center of the shrimp for a time period sufficient to destroy active and inactive bacteria such as Listeria. The precooked shrimp are then discharged into an automatic shrimp peeling machine for subsequent processing.
2. Description of the Prior Art
Effective peeling of precooked coldwater shrimp such as Pandalus Borealis has remained essentially unchanged since its inception and development by a Mr. Blomstrom in Sweden in approximately 1959. Various refinements have been made in the apparatus for precooking coldwater shrimp. U.S. Pat. No. 3,383,734 issued to James M. Lapeyre on May 21, 1968 and U.S. Pat. No. RE.26,971 issued Oct. 20, 1970, discloses a cooking hood suspended over an inclined conveyor belt which moves unpeeled shrimp to the entry point of an automatic shrimp peeling machine. In this patent, perforated steam pipes are located above the shrimp so that steam is forced downwardly onto the shrimp prior to the shrimp entering the peeling machine.
U.S. Pat. No. 3,581,652 issued on Jun. 1, 1971 to J. A. Chauvin discloses apparatus for shrimp to be cooked by steam condensate (flash steam) rising above boiling water at atmospheric pressure, as shrimp are moved on a porous conveyor belt through a single cooking zone covered with a hood.
U.S. Pat. No. 4,887,524 issued to Roy Ellis-Brown requires heat and pressure generated from steam directed upwardly within a housing under a conveyor belt with the shrimp being precooked in steam condensate (known as "flash") at a temperature always under 212.degree. F.
U.S. Pat. No. 4,862,794 issued to George C. Lapeyre et al. on Sep. 5, 1989 discloses shrimp being cooked in an airless atmosphere under pressure at a temperature ranging between 180.degree. F. to 212.degree. F. in a single automatically controlled heat zone which does not permit controlled cooking temperatures when the automatic steam control valve varies the steam flow from on to off or partially on to off and as a result varies the cooking heat on the shrimp from 180.degree. F. to 212.degree. F. at all times during operation resulting in historisis which is the rate of response and degree of variation is not commensurate with the rate of product flow. It is well known to those in this art that tissues in the shrimp begin to breakdown when cooked by steam above atmospheric pressure. This results in a limited shelf life of canned shrimp which is one of the results of cooking shrimp under pressure None of the prior art prevent historisis and none of the prior art provides any apparatus to obtain quick constant high temperature for a time and then lower temperature equilibration for a time.